Electrode catheters have been in common use in medical practice for many years. They are used to stimulate and map electrical activity in the heart and to ablate sites of aberrant electrical activity. Atrial fibrillation is a common sustained cardiac arrhythmia and a major cause of stroke. This condition is perpetuated by reentrant wavelets propagating in an abnormal atrial-tissue substrate. Various approaches have been developed to interrupt wavelets, including surgical or catheter-mediated atriotomy. Prior to treating the condition, one has to first determine the location of the wavelets. Various techniques have been proposed for making such a determination, including the use of catheters with a mapping assembly that is adapted to measure activity within a pulmonary vein, coronary sinus or other tubular structure about the inner circumference of the structure. One such mapping assembly has a tubular structure comprising a generally circular main region generally transverse and distal to the catheter body and having an outer circumference and a generally straight distal region distal to the main region. The tubular structure comprises a nonconductive cover over at least the main region of the mapping assembly. A support member having shape-memory is disposed within at least the main region of the mapping assembly. A plurality of electrode pairs, each comprising two ring electrodes, are carried by the generally circular main region of the mapping assembly.
In use, the electrode catheter is inserted into a guiding sheath which has been positioned a major vein or artery, e.g., femoral artery, and guided into a chamber of the heart. Within the chamber, the catheter is extended past a distal end of the guiding sheath to expose the mapping assembly. The catheter is maneuvered through movements that include deflection of a distal portion of the catheter so that the mapping assembly is positioned at the tubular region in the heart chamber. The ability to control the exact position and orientation of the catheter and also the configuration of the mapping assembly is critical and largely determines how useful the catheter is.
Steerable catheters are generally well-known. For example, U.S. Pat. No. Re 34,502 describes a catheter having a control handle comprising a housing having a piston chamber at its distal end. A piston is mounted in the piston chamber and is afforded lengthwise movement. The proximal end of the elongated catheter body is attached to the piston. A puller wire is attached to the housing and extends through the piston, through the catheter body, and into a tip section at the distal end of the catheter body. The distal end of the puller wire is anchored in the tip section of the catheter. In this arrangement, lengthwise movement of the piston relative to the housing results in deflection of the catheter tip section.
The design described in U.S. Pat. No. RE 34,502 is generally limited to a catheter having a single puller wire. If bi-directional deflection is desire, more than one puller wire becomes necessary. Catheters adapted for on-plane bi-directional deflection are also known. A flat beam is normally provided to enable deflection on both sides of the beam within a plane. However, the puller wire in tension under deflection often flips over to the other side of the beam, or where the puller wires are located close to the beam, a large bending moment is required to deflect the beam, imposing significant stress on the puller wires. Moreover, with the puller wires close and tightly constrained to the beam, adhesion failure or rupture of the constraint poses a risk.
The employment of a pair of puller wires to effectuate bi-directional deflection also required a number of components which occupied space in a space-constrained catheter. More components also increased the risk of component failures. The use of T-bars and/or crimps can unduly fatigue puller wires and impart shear stresses resulting from skewed or off axis alignment of puller wires relative to the longitudinal axis of the catheter, even if by a minor degree. While bi-directional deflection is unquestionably an improvement over uni-directional deflection, bi-directional deflection is typically symmetrical whereas many regions of the heart lack symmetry. Thus, it would be desirable to provide a catheter with more deflection variety and options.
Accordingly, a need exists for a catheter capable of predictable on-plane nonsymmetrical bi-directional deflection which employs fewer components while still enabling mapping and/or ablation capabilities. A need also exists for a catheter employing a flat deflection beam which can be deflected easily without significant tensile or shear stress on the puller wires.